The present invention relates to a pulse combustor for the generation of heat energy by self-generating repetitive cycles of combustion of a combustible fuel.
A combustor is a device for burning gaseous, liquid or solid fuel to produce heat which, in turn, is used for heating other materials or to consume combustible waste products. Operation produces a significant change in gas pressure and/or velocity which is used to do work.
There are two distinct categories of combustors, namely conventional and pulse combustors. In conventional combustors air and fuel are introduced into a combustion chamber, compressed and ignited in a continuous process. A major problem with conventional combustors is in achieving stability of the flame used to ignite the fuel because of the required air/fuel ratios. A high air/fuel ratio is needed to optimize turbine efficiency and for controlling efficiency. The principal type of conventional combustor used for turbines consists of an open ended can into which compressed air is directed. Some of this air is channeled into an outer annulus while the remainder is forced through the center. Fuel is introduced by various means such as atomization by a spray nozzle into the center stream of air and ignited by a burner flame. The additional air flowing through the outer annulus is introduced downstream of the flame through various scoops, openings, baffles and diverters in order to maximize the air/fuel ratio and yet keep the flame stabilized by operating at a lower air/fuel ratio in the burner region. In addition to the difficulty in maintaining flame stability, such combustors exhibit several design problems which make the device complex and costly. Gaseous and liquid fuels may be burned but solid fuels such as pulverized coal may not.
A simpler and less costly alternative to a conventional combustor is a pulse combustor. In simple pulse combustors a mixture of air and fuel is initially ignited by a spark from a spark plug. The gases explode, producing a steep pressure rise and temperature increase followed by exhaustion of the gases and a subsequent pressure drop. Cooling by heat exchange at the chamber walls enhances the pressure drop. Reduction of the pressure results in some atmospheric air, fuel and a small portion of the exhaust gases still in the exhaust region to be sucked back into the combustion chamber. The high temperature still present in the chamber causes the new mixture to ignite, repeating the process with pressure waves performing the function of pistons. Known pulse combustors are linear structures in which the exhaust gases and pressure waves resulting from ignition travel down a tube and on the suction phase atmospheric air and some exhaust gases return. Some linear combustors employ valves to obtain positive shut off and thereby obtain higher pressures. Linear pulse combustors are smaller and lighter than conventional combustors for an equivalent power output. However, linear pulse combustors can not be scaled to produce a wide range of outputs. Smaller units tend to perform poorly relative to larger units. In general, linear pulse combustors have high combustion efficiencies, a high thermal efficiency and have low pollutant production, particularly in NO.sub.x species. However, they are relatively noisy and vibrate excessively. Once optimized for best overall performance, it is difficult to operate a linear pulse combustor at a partial load. Linear pulse combustors are unable to operate on fuels having a low latent heat of combustion if designed to operate on fuels having a high latent heat of combustion.
Accordingly, it is an object of the present invention to provide an improved pulse combustor. It is a further object of the present invention to provide a pulse combustor of simple design. It is yet a further object of the invention to provide a pulse combustor capable of operation over a wide variety of sizes and a wide range of loads and values of heat production of the fuel.